In this study, the effect of Rhizoma Alismatis on experimentel fat rat caused by monosodium glutamate which was injected hypodermically at large doses into fant rats has been observed.The conclusion of experiment shows that the rat weight increased, the Lee exponent value was obviously larger than that of control group, the fat in body was accumulated in abundance and the content of serum triglyceride markedly rose after 10 weeks when monosodium glutamate was injected. The Rhizoma Alismatis can reduce Lee exponent value of fat mice, fat exponent and serum triglyceride content in periphery of uterus and testis, which suggested that it possessed a certain action against fat.